There is a high prevalence of depression in HIV-infected populations, as well as in some HIV-uninfected populations at risk for HIV. Depressive symptoms themselves have been associated with behaviors that transmit HIV infection. The aim of the proposed cross-sectional study to define the epidemiology of depression, as well as any substance use disorders that may interact with depression in those attending an inner city STD clinic who are known to be at high risk for acquiring HIV. Those who present with symptoms of a new STD or as an STD contact will be eligible for enrollment. They will undergo (1) screening for depression using the Beck Depression Inventory and General Health Questionnaire; (2) behavioral assessment for HIV transmitting behaviors by confidential computer-based survey; and (3) clinical and laboratory evaluation for STDs. Of the 700 enrolled participants, 200 will additionally undergo a structured clinical interview in order to establish a specific DSM-IV diagnosis. The data generated will allow us to describe (1) the prevalence of major depression and substance use disorders in an STD clinic population at high risk for HIV; (2) the independent association of depression with behaviors that transmit HIV infection; (3) the independent association between depression and biologic measure of risk, an STD diagnosis.